Help with Code 33 on a 1990

[brandywine]

Hi all,

I have a 1980 with mildly modded ZZ4 and TPI. The PCM/ECU is from a 1990 and is a MAP system, not MAF.

I am getting an intermittant error code 33 - MAP voltage high - low vacumn. The engine runs normally, and then starts to run rough -hesitate/stumble. Within a few minutes the problem seems to clear up, but system is running in open loop. This has happened twice in the last 3 weeks. I have a scanner tool that I can use to read the codes, see the voltage, erase codes, etc.

I erased the code the first time and waited to see if it would come back. It took about 3 weeks. The problem seems to occur when the car is at operating temperature with a load.

The MAP sensor at idle is at 1.61V. With the engine off and the ignition on the MAP sensor reads 4.78V.

I have taken the MAP sensor off and inspected the plastic module and the hose that runs to the plenum for cracks or leaks. None found.

Does anyone have any diagnostics on this particular year/code (1990) that they can post. I'm not a TPI expert, so use small words...

Thanks in advance.

 

[vetteoz]

Has computer been tuned for ZZ4 cam?.What are your idle revs?
Note it states unstable idle may cause DTC 33

DTC 33 is MAP signal high indicating low vacuum
Your idle V look a little high which means the computer is "seeing" a lower vac reading with the throttle closed than what it expects to.


For a LT1 but same
http://www.fastbird93.com/diagnostics/dtc33p1.jpg
http://www.fastbird93.com/diagnostics/dtc33.jpg

 

[brandywine]

Hi OZ,

The chip has been tuned for my ZZ4 setup...

Requested idle after warm-up is 725rpm...idles between 725 and 750 with 1.6V coming from the MAP sensor.

Problem is not noticable at idle, only while under load in gear.

Thanks for the diagnostics.

 

[aklim]

Check the IAC counts to see if it is trying it's best to compensate for the new cam. If it cannot go thru the IAC it will probably try timing and fuel.